fix: hoist constraints on inputs to top of program (#4076)

# Description

## Problem\*

Followup to #4065 

## Summary\*

This PR fixes a small mistake in #4065. I mixed up the front and back of
the vector for the case where we don't find an instruction for which the
constraint's inputs are a result. This results in constraints on the
program inputs not being pushed up to the beginning of the program.

This PR fixes the index to insert these instructions so that we
constrain the inputs first.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_evaluator/src/ssa/opt/bubble_up_constrains.rs

@@ -30,7 +30,7 @@ impl Ssa {
                         // We iterate through the previous instructions in reverse order so the index is from the
                         // back of the vector. Subtract from vector length to get correct index.
                         .map(|reversed_index| filtered_instructions.len() - reversed_index)
-                        .unwrap_or(filtered_instructions.len());
+                        .unwrap_or(0);
 
                     filtered_instructions.insert(index, instruction);
                 }

test_programs/execution_success/bit_and/Prover.toml

@@ -1,2 +1,4 @@
 x = "0x00"
 y = "0x10"
+a = "0x00"
+b = "0x10"

test_programs/execution_success/bit_and/src/main.nr

@@ -1,6 +1,6 @@
 // You can only do bit operations with integers.
 // (Kobi/Daira/Circom/#37) https://github.com/iden3/circom/issues/37
-fn main(x: Field, y: Field) {
+fn main(x: Field, y: Field, a: Field, b: Field) {
     let x_as_u8 = x as u8;
     let y_as_u8 = y as u8;
 
@@ -9,8 +9,8 @@ fn main(x: Field, y: Field) {
     let flag = (x == 0) & (y == 16);
     assert(flag);
     //bitwise and with odd bits:
-    let x_as_u11 = x as u11;
-    let y_as_u11 = y as u11;
-    assert((x_as_u11 & y_as_u11) == x_as_u11);
+    let a_as_u8 = a as u8;
+    let b_as_u8 = b as u8;
+    assert((a_as_u8 & b_as_u8) == a_as_u8);
 }